The present invention relates to an injector particularly for a vacuum die-casting apparatus.
In recent years, light alloys are being used increasingly to manufacture structural components and/or elements, such as for example chassis and body components of assembly-line vehicles.
The die-casting process consists in keeping the material in the molten state in a holding furnace, in subsequently transferring a specific amount thereof into an injector for injection in a die, and in finally cooling the resulting casting.
In vacuum die-casting, a vacuum is produced before introducing the molten material in the die.
In terms of plant maintenance and amortization costs, the die-casting process is highly advantageous if it relates to the production of large batches meant for high-volume mass-manufacturing lines.
Standard die-casting apparatuses, however, are scarcely suited for the production of vehicle frame or body components due to their brittle fracture behavior and to the porosity of the resulting castings.
It is in fact currently impossible to produce Alxe2x80x94Mg alloy castings, since castings full of porosities are obtained, with a high number of gas inclusions.
Brittle fracture, porosity and inclusions are unacceptable in castings which should be welded and which are required, in various forms, to have high plastic deformation properties.
The main limitations of the die-casting plants currently in use include the structure of the injectors used and the injection technique.
Injectors currently in use are constituted by an injector body provided with an opening for loading the liquid material and with a chamber for containing the material and for the sliding of a piston for injecting the material into the dies.
A lubricant is usually introduced in the containment chamber.
However, the lubrication of the chamber cannot be controlled and is therefore unreliable from the point of view of the process.
The presence of residues of lubricating material produces porosities and/or the formation of oxides which no longer ensure the quality of the casting.
Moreover, during the loading of the molten material into the chamber of the injector body the material is continuously in contact with a contaminating atmosphere which can cause the generation of oxides and therefore the formation of gas inclusions inside the casting.
Another cause of porosities and inclusions is the turbulence of the liquid material which is caused when the material is poured into the injector body.
The aim of the present invention is to solve or substantially reduce the problems of conventional injectors.
Within this aim, an object of the present invention is to provide an injector by virtue of which it is no longer necessary to introduce lubricating material inside the injector body in the containment chamber.
Another object of the invention is to provide an injector by virtue of which it is possible to work in a protective gas atmosphere.
Another object of the invention is to provide an injector which allows to produce equally thin-walled or thick-walled die castings.
Another object of the invention is to provide an injector which allows to use innovative alloys which otherwise cannot be used in conventional apparatuses.
This aim and these and other objects which will become better apparent hereinafter are achieved by an injector particularly for a vacuum die-casting apparatus, characterized in that it comprises an injector body provided with at least one first opening for injecting/aspirating a protective gas, and at least one second opening for loading molten material, which are arranged in order of operation, said injector body being further provided with a chamber for containing material and for the sliding of a piston for pushing the material into a die, said injector comprising means for cleaning and lubricating the external surface of the piston which are arranged in order of operation on a corresponding supporting element which is separate from the injector body.